Although
the ability of salmon to return to a home stream may depend
on a variety of cues, most researchers believe that scents within
the water are the primary cues the fish rely on for homing to
a specific stream. Scientists believe the specific odor cues
of a stream might be embedded within the genetic makeup of each
fish. Factoring in this possible genetic influence is critical
when raising new stocks.

A
cooperative challenge in which students work together to uncover
a series of trails

Finding
Your Way
In this activity, students will be challenged to record a path based
upon olfactory cues. Scents placed at critical junctures will set
the fixed path that each team must follow.

Materials

Paper cups

Paper
towels

Pencil

Yard
stick

Five
different and distinct scents

Yarn

Tape

NOTE:
To best perform this activity, the class should be divided into
two groups. One group creates the scent trails. The other group
uncovers them.

Before
You BeginThe
activity is performed on a grid that has been laid out on a large
flat surface area (such as a gymnasium floor.) To build the grid,
you'll need to use a yard stick and tape. Each line of the grid
is separated by one yard. In addition, the distance between neighboring
grid points (marked by a taped "X") is also one yard. Using the
same distances, identify both the staring point and the home stream.
Here's what the completed grid looks like:

Steps
(For the set-up)

Work in teams of two. Obtain a homing scent from your instructor.

Obtain seven paper cups. Use a pencil or other sharp object
to carefully punch several holes into the cup.

Crumble a piece of paper toweling and stuff it into the cup.

Add several drops of your scent to the paper toweling.

Invert the cup and place one cup at any of the grid "X"s.

You'll need to agree with other teams on cup placement.Place
a second cup on the next line. Try to mix up the positions so
a zigzag pattern emerges.

Keep placing your scented cups until one has been positioned
on each of the five lines.

Don't forget to place one cup at the starting line and another
at the "home" target.

Make a record of this pattern.

Here's what the punched cup over the mark looks like:

Steps
(For uncovering trails)

Work in groups of two. Randomly select one of the five scents.

Begin at the starting point. You should have a long length of
yarn and a roll of adhesive tape.

When the instructor gives the signal, find the cup in the first
line that contains your assigned scent.

Tape one end of the yarn to spot where your starting cup is
positioned.

Move on to the next row. Locate your scent cup. Continue to
lay down a yarn trail and tape it to the appropriate spot.

Continue uncovering and recording your scent trail until you
reach the finish.

Make sure that all of the scent trails have been completed and
all the cups used in determining the separate and distinct trails.
Here's an example of what the finished the finished scent trails
might look like.

Questions

Why was it necessary to punch holes in the scent cups? (You needed holes through which the odor could escape.)

What was the purpose of the yarn?(It was used to record the travel from the start to the finish.)

What was the purpose of the cups? (They were odor landmarks on which the course was based.)

Communicating
by Dance
Could you demonstrate the homing of salmon by choreographing and
performing a dance? In addition to the fish, make sure to include
scents and several branching streams that support different salmon
populations.

Genetic
Window?
Is the ability to detect certain odors in humans genetic? Is your
immediate family more sensitive to certain odors than members of
another family? With your instructor's approval, design a strategy
for inquiry that would explore this relationship. Create a controlled
experiment that might show if there is a genetic component to sensitivity
to different odors.

Diluting
Odors
How does diluting odors affect a person's ability to detect them?
Think about it. Then, with your instructor's approval, design an
experiment that would test how a dilution of different scents affects
their ability to be detected. Use a variety of odors. Which ones
can be diluted most and still be detected? Which odors become undetectable
with even the slightest dilution?